I have a 2000 Bonneville 3.8. My problem is that at highway speeds there is a vibration in the car, but not the steering wheel. No tire inbalances. When i grab the CV joint near the trans i can move it up an down at least a 1/4 inch. Is this normal or is there a bearing going bad in the trans axle? Other side has play, but half as much. How much play is normal there? If it bad how bad is that to replace?

I can't say about the play being normal or not, but I do know that vibration in the 2000 + Bonneville'* is a very common problem. Ours has it also ( 2003 ) at about 65 - 75 MPH.

We have had people get their tires balanced two or three times and still have problems. It seems that some people have had luck with a road force balance, where the machine actually applies pressure via a roller to the tire during the balancing process.

Not sure if that helps, but might be worth looking into.